It is conventional to equip a headlamp with means for adjusting its beam in the horizontal direction and/or the vertical direction (i.e. in azimuth and/or in elevation, respectively). It is also conventional to preset in the factory a "zero" position or reference orientation. Fine adjustment can be carried out subsequently, either manually or with the aid of a motor, within a predetermined range of angles with respect to the reference orientation.
It is known in the prior art to employ various means which are attached in the workshop to abutments or the like which are provided on the vehicle, so as to indicate the deflection or orientation error with respect to the reference orientation, according to the position of the headlamp housing or that of the reflector which is enclosed within the housing. In this connection, reference is invited to French published patent specification FR 2 658 293A. This arrangement does however have the disadvantage that it requires the use of special orientation indicating means. These are separate from the vehicle and may therefore be mislaid, or unavailable, and so on. They may indeed become wrongly positioned on the vehicle, and this gives rise to errors in the indication of beam orientation.
Another known arrangement consists in providing, on the headlamp, means for permanently retaining a "memory" of the reference orientation as set in the factory during assembly, arranged in such a way as to indicate both the reference orientation and also the deflection or error with respect to the reference orientation.
An adjusting and indicating knob, which enables this requirement to be satisfied, is also known from French published patent specification FR 2 664 963A. Such a knob does however have quite a complex and inconvenient construction.
Finally, it is also known to provide orientation indicating means which are mounted on the reflector, and which lie at least partially within the housing of the headlamp, which makes it necessary to provide in the housing a transparent observation window, and which makes reading somewhat difficult.